Sildenafil, disclosed in WO9428902, is first kind of orally-administrated potent inhibitors of phosphodiesterase 5 in treatment of the erectile dysfunction of man. By inhibiting the phosphodiesterase 5 in corpus cavernosum, it can achieve the purpose of relaxing smooth muscle in human corpus cavernosum, improving penile hyperemia so as to result in erection. The effective rates of sildenafil in treating male sexual organs erectile dysfunction amount to 80%.
Also, Pfizer Ltd. has developed a series of 1,6-dihydropyrrol[4,3-d]pyrimidin-7-one derivatives, and broadened their therapeutic area where such indications was thought to be treated by inhibiting phosphodiesterase 5. All of these compounds are disclosed in EP0951098, WO9849116, U.S. Pat. No. 6,251,904, and WO0024745, and the latter two of patents include the compounds whose substituted phenyl on C-5 is replaced by the substituted pyridin-2-yl. On the basis of the structure of Sildenafil, DONG A PHARMA Co. Ltd. of Korea developed a series of mono substituted derivatives in the nitrogen atom of sulfonylamino group, as disclosed in WO0027848 and WO0198304. Presently, as described in WO0216364, in order to further enhance water-solubility, LG Chem. Invest. Ltd. disclosed the derivatives of 1,6-dihydropyrrolo[4,3-d]-pyrimidin-7-one with polyethylene glycol. In addition, 1,5-dihydropyrrolo[3,4-d]pyrimidin-4-ones and 1,9-dihydropurin-6-ones were developed by Pfizer Ltd. for the treatment of sexual dysfunction (U.S. Pat. No. 6,100,270). WO0160825 disclosed 3,5-dihydropyrrolo[3,2-d]pyrimidin-4-ones are useful for the treatment of impotence. Recently, 3H-imidazo[5,1-f][1,2,4]triazin-4-ones was disclosed by Bayer Co. Ltd. in the patent application DE19881732.